Force/Update Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Moby leads a blindfolded Tim to an airport runway. TIM: Man, I can't wait to see what my birthday activity is this year. MOBY: Beep. TIM: You're the best robot pal a kid could ever– Moby removes Tim's blindfold. Tim sees they are at the X-Treme Rush Skydiving Center. TIM: No! MOBY: Beep. TIM: I... I think I might just answer this letter. Tim reads from a typed letter. TIM: Dear Tim and Moby, if forces are invisible, how do we know they exist? And how do they work? Thanks, Katelin C. Forces are at work all the time, acting on everything around us. We can't see them, but some of their effects are pretty obvious. Like any time an object changes speed or direction. A split animation shows a skydiving man pulling his parachute cord and an overhead view of a plane making a turn on a runway. MOBY: Beep? TIM: At its most basic, a force is a push or a pull. And it always involves two or more objects. Something providing the push or pull, like Moby. And the thing it affects, like, um, me. Moby is trying to push a resisting Tim toward an airplane hangar. MOBY: Beep? TIM: Well, it's never really that simple. Objects usually have lots of forces acting on them at the same time. Each one has a magnitude, the size of the force, and a direction. Put in fancy science terms, we say force is a vector quantity. Arrows point toward each other below Tim and Moby. The arrows are different colors, red under Tim, green under Moby. MOBY: Beep. TIM: Like right now we are pushing equally hard, in opposite directions. Our forces are in balance, canceling each other out. That's why I'm not moving. The sum of the forces, or net force, is zero. MOBY: Beep? A dial appears above the arrows and points to zero. TIM: Zero Newtons to be precise. That's the unit we use to measure force. Both Moby and Tim's arrows are labeled "100 N" and "Newtons" appears on the dial. TIM: It's named after Isaac Newton, the physicist who figured a lot of this stuff out. Newton appears and winks. MOBY: Beep. TIM: To get me in motion, you'd need to exert an unbalanced force on me. Aaack! That's any push or pull where the net force is not zero. Moby pushes Tim forward. The dial measures 100 on Moby's side and his arrow reads 200N versus Tim's 100N. Moby then walks Tim to an old propeller plane that has a robot pilot. PILOT: Twang. TIM: I am not getting in that thing! Tim and Moby appear inside the plane wearing skydiving gear. TIM: What?! Moby places a helmet on Tim's head. MOBY: Beep? TIM: You're just trying to distract me, but fine. The plane is taxiing on the runway. TIM: Right now, there are three main forces accounting for our movement. The engines are pulling the plane forward. A thick green arrow points in the direction the plane is moving. TIM: There's friction, the resistance a surface puts on anything sliding over it. A thin red arrow points to the wheel in the opposite direction of the plane's movement. TIM: And drag, which is basically the friction of air molecules. A thin red arrow points above the plane in the opposite direction of the plane's movement. MOBY: Beep? TIM: Yeah, you would think the force of the engines must be greater than friction and drag. After all, we're moving forward. A greater than sign is placed between the thick arrow representing the engine's force, and the two smaller arrows representing friction and drag. TIM: But notice how still it feels in here? If the forces were out of balance, we'd feel the push. And we'd be able to observe its effects. Moby throws an apple. MOBY: Beep? TIM: Well, we'd see a change in the plane's speed or direction. The combination of these two values is called velocity. We're not speeding up or slowing down. And we're heading in a straight line. A split animation shows the plane's dial reading a steady 40 and an overhead view of the plane taxiing on a runway. TIM: So, the net force on the plane is zero, same as if we weren't moving at all. As the plane taxis down the runway, an equal sign is placed between the arrow representing engine forces and the arrows representing drag and friction. The Newton dial reads zero. TIM: We're gonna need to accelerate if this hunk of junk is gonna get off the ground. PILOT: Twang. The pilot looks back at Tim and Moby and pulls a lever up. Tim and Moby, sitting in sideways placed seats, lean toward the back of the plane as it accelerates. TIM: In physics, acceleration isn't just speeding up. It's any change in velocity, including speedups, slowdowns, and turns. Split views show the different ways Tim and Moby's bodies react to the types of acceleration Tim describes. TIM: There's a reason you can feel it when a car, or a plane, accelerates. It means there's an unbalanced force being applied to it, and to you. The plane lifts off. MOBY: Beep. TIM: Yup, the plane has to generate enough upward force to overcome gravity. It's a little different than the forces we've talked about so far. An upward pointing green arrow appears above the plane, a downward pointing red arrow below it. TIM: Friction, drag, you pushing me, those are all contact forces. They're between objects that are touching. Images illustrate these forces. TIM: Gravity is a non-contact force: it can affect objects that are separated, like the earth and this plane. A view from space shows arrows representing gravity pointed toward the earth. TIM: Magnetism and the electrical force are non-contact, too. Images show north and south poles of a magnet attracting each other, and negative poles attracting positive poles in electrical forces. MOBY: Beep. TIM: Like all non-contact forces, gravity acts through a field: an invisible area of influence. Fields get weaker the farther out you go from their source. An image of fields around the earth illustrates what Tim describes. TIM: But even way up here, Earth's gravitational field is still plenty strong. Which is why I am absolutely not goooooooo..... Tim goes into slow motion after Moby bumps him out of the open door of the plane. His face becomes distorted from the wind. Moby looks at him from out of the plane, then jumps and falls into a controlled dive. TIM: Aahhhhhhhh! MOBY: Beep. Moby is next to Tim as they both free fall. TIM: Oh, hi. Moby opens a panel in his arm. A Newton dial points to 1000. TIM: Yep, the gravitational force is pulling us down, hard. Thick downward green arrows appear underneath each of them. TIM: It's opposed by drag, which is resisting our downward motion. Thinner upward red arrows representing drag appear above them. TIM: The two forces are way unbalanced; that's why we're still accelerating. But the faster we go, the more drag increases. The upward arrows get thicker while the downward arrows get slightly thinner. The downward arrow is still thicker than the red. TIM: Eventually, those two forces will fall into balance. There we go. The upward and downward arrows become the same thickness. MOBY: Beep? TIM: Our velocity is steady, which means we've stopped accelerating. So the net force on us is now zero. The Newton dial in Moby's arm reads zero. TIM: That's why it doesn't feel like we're falling anymore. More like floating. MOBY: Beep? TIM: When we pull our cords, our parachutes will increase drag. So there will be a sudden unbalanced force upward. Right after Tim and Moby pull their cord, the upward arrow representing drag becomes very thick. They go from a lying down position with arms raised to standing position. TIM: But as we slow down, drag decreases. Eventually, drag and gravity balance again, and our velocity levels off. The upward arrows thin out and become the same size as the downward arrows. TIM: Hey, you know what? This was the best birthday present ever. MOBY: Beep. A birthday cake attached to a parachute appears between Tim and Moby. TIM: Oh, you. A heart shape encloses them as they descend towards the ground Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts